The ultimate objective of this study is to elucidate the endocrine function of relaxin and to determine which of the structural features of the hormone is essential for the response in the target cells. The investigation will include the study of the mechanism of biosynthesis of relaxin, its secretion and transfer to the target cells. Experiments have been designed to elucidate the mode of relaxin-receptor interaction and the nature of the primary cellular response to relaxin stimulation. Another aspect of this work will be concerned with the mechanism of the macromolecular remodelling of the symphysis pubis, the major target organ of relaxin. Finally an attempt will be made to determine whether relaxin mediates its response via a different factor or whether relaxin itself is a factor dependent upon growth hormone for its action. Structural studies of the shark relaxin from Odontaspis tauris will be continued.